Method for printing cinematographic films



METHOD FOR PRINTING CINEMATOGRAPHIG FILMS Filed Jan. '7, 1952 @EA/$177 0F 6647705 ATTORNEY Patented Mar. 12, 1935 UNITED STATE METHOD Foa PRINTING omEMATo- GBAPHI CFILMS Paul ,Vanet, Le Vesinet, France, assigner to Le Film Ozaphane, a corporation of France Application January 7, 1932, serial Nt. 585,322 In France February 16, 1931 3 Claims.

This invention relates to a method for printing cinematographic films.

, There are now to be found in the trade lms and photographic papers in which the material sensitive to light comprises a diazo derivative or a stable'mixture of a diazo'derivative andan azo.

component.

In the rst case, ing an amine or aphenol in an alkaline medium to act on the film `or'on `the paper after exposure tothe sun; in the second case it is suicient to ltreat the paper or thefllm by means of a gaseous alkali or by an alkaline solution after exposure to the sun.

.The lms or papersso prepared yield uninverted images, that is to 'say a positive is reproduced as a positive and a negative yas a negative. It is found, however, that when. prints are used which would give correct reproductions on a silver bromideV sensitive nlm, the images obtained on a film which has been sensitized with a diazo compound', show a faulty grading.

In order to discover-the cause of this abnormal result, I have been led to investigate the manner in which the light actson the films or papers sensitized by means of diazo `derivatives and I have found that the value of the optical densities obtained in function of the amounts of light is goverened by a law which widely departs from the law obtainedfor silver bromide emulsions. It should be remarked, rst'of all, that said law generally proceeds inversely of the one obtained for bromide, sin'cediazo compounds yield uninverted images. y l In order to more clearly describe my invention, I have shown several 'curvesun the drawing representing the characteristics of various films.

In the drawing: Figure l shows a' set ofy curves disclosing the comparative results obtained by varied times of exposure. f

Fig. 2 shows a .curve corresponding to a different density. Fig. 3 shows' a curve correspondingto a still different density.

For the`sake of .convenience and for abetter comprehension of the explanations which will be given hereinafter, I shall trace the characteristic curve representative of the action of light on diazo compounds, plotting as abscissae the optical densities of a neutral grey corner the densitiesv of which go on increasing from zero,' and as ordinates the densities obtained with the diazo compound behind the densities of said. neutralthe image is obtained by caus- -to one another.

grey corner. The duration of exposure to light will be the same for allparts of the printing.

. It is-to be noted that this method of construct- 'ing the characteristic curve is, in point of fact, just, equivalent to the method of Hurter and Drifeld, 'since the axis of the absciss-figures from right to left lengths which are proportional to the logarithms of the amounts of light trans- I In treating diazo compound .sensitized lms, the 10 developmentsmust be carried so far as to developI the whole ofthe remaining diazocompound, such a protracted development having no eect on the results. Too short a development would leave some diazo compound untransformed into a dye 15 and should always be' considered` as defective.

A, If, for a transparent film sensitized with any given diazo compound, I construct the curves corresponding to various and increasing times ofexposure ti, i2', lta, I obtain a sheaf of curves 20 c1, c2, c3- such as those shown in Figure 1,'which are all similar as to shape but offset with respect v Curve c1 will correspond to an underexposure, since the'high lights of the 'negative will have `a density equal to 1. Curve c2 will 25 the curve c2, and' being so determined that it be just sufcient to destroy', the `whole of the diazo 35 compound behind density 0 of the neutral grey corner or, more precisely, behind the light density corresponding to a highlight of. the negative.

In practice there will be obviously a slight tolerance as to the exact value of this vtime of ex-` posure'. A

A silver bromide emulsion permits, for a'given time of exposure, of `obtaining a series of curves the gamma of which variesiaccording tothe time of develpment while a diaz derivative yields but a singlevcurve. Widely different working conditions should, therefore, be expected with the diazo derivative. A

As will be apparent, a lm sensitized by means of a given amountof diazo compound is characterized rstly by the fact that, on being thoroughlyldeveloped without having undergone any exposure to the sun, it will yield a maximum density corresponding to an asymptote'whieh will be horizontal to the characteristic curve. The

latter shows a portion which is substantially rectilinear up to a value equall` to 2/3 or at most to 3A of the maximum density. If We consider the curve cz of Figure 1 which corresponds to a sensitive film adapted to yield a maximum density equal to 2.0 it will be ,seen that only the portion of the corner having a density increasing from to 1.0 will provide a correct rendering of the densities, the contrast factor excepted, while the rest of the corner is rendered in a defective manner.

In the same way (Figure 2), on the curve corresponding to a density 0f l3.0 it will be seen that there will be obtained a range o densities correctly increasing from 0 to 2.2 behind the densities of the print increasing from 0 to 1.0, that is to say for illumination values comprised between the value which produces complete discolouring and about one tenth of this value, while beyond there is no longer any proportionateness between the densities of the print and the densities afforded by the diazo compound.

Lastly, a curve such as the one shown by Figure 3 corresponding to a film sensitized by means of a diazo compound inI such a way as to provide densities which will exactly reproduce those cf the corner between values 0 and 1, that is to say corresponding for this portion to a gamma value equal to unity, will permit ofcbtaining only a maximum density equal toabout 1.4 with an incorrect rendering for all the portions of the print whose density is superior to 1.0. This sort of sensitizing corresponding to the curve shown by Figure 3 is, indeed, the one which has hitherto been prepared by means of diazo compounds.

Now, in cinema practice, it is generally admitted that the image of a positive film properly printed should offer shadows having a maximum density about 2.0 corresponding to the average of good prints the subjects of which, having a variety of luminosity comprised between 1 and 100 or thereabout, are rendered with a product of the gamma of the negative and of the positive equal to unity. Therefore, in order to obtain on a lilm sensitized by means of a diazo derivative a correct rendering of the images, the following two conditions will have to be performed.

.1. To determine for the diazo compound in question the amount to be used for sensitizing the lm in such a way as to have a maximum'density of about 0.7.

2. To make the positive print which will serve as a matrix with a gamma value sufficiently low in order that the maximum shadow may have a. density capable of giving a density equal to 2.0 onthe diazo compound.

Practically, in the case contemplated, the value of the maximum density of the positive print, i. e. about 1.0, corresponds to a value of gamma of about 0.5.

Of course, the prints are to be made while using as much as possible the rectilinear portion of the characteristic curve of the silver bromide emulsion and while preferably using an emulsion the characteristic curve of which shows a very long rectilinear portion.

The interest which attaches to my invention resides in the fact that. hitherto, films sensitized by means of diazo compounds were prepared with a low maximum density giving hardly sharp but rather mealy images. As a matter ol" fact a density of 1.6 was never exceeded, so that the prints Used which had themselves a maxi-- mum gdensity of about or even above 2.0 with a gamma of about 1. would yield images without any contrast in the shadows, even when these prints were entirely made on the rectilinear portion of the silver bromide emulsion.

Of course,v the use, for printing diazo compound films, of positives having, in the deepest shadows, a maximum density higher than 1.0 but inferior to a limit which may be stated as 1.8, affords an appreciably better general grading ofthe images and for printing diazo compound sensitized lms, I claim the use of positives having a maximum density inferior to 1.8 for a. subject the luminosity values of which range from 1 to 100 or thereabout.

Taking the foregoing into account, it becomes obvious that the correlative increase of maximum density which can be afforded bya diazo compound sensitized lm already provides a bettering of the grading from a value the minimum of which may be xed at 1.6.

It is also obvious that the foregoing considerations are particularly applicable to iilms -the images of which show a black or very dark hue, such as a sepia brown or blackish blue, in a word, for colours where sight will readily make, with negligible error, -comparative measurements of densities by taking neutral grey as a standard for comparison. Besides, the remarks which have been made will remain applicable, all else remaining equal, 'when using corners Amade of a colour identical to the one desired to be compared.

Obviously the conclusions arrived at might be extended to the case where a correct rendering is desired to be effected up to a density value superior to 2.0.

'Ihe prints or matrices prepared pursuant to the above set forth principles are practically unsuitable for obtaining proper prints on silver salts, supposing it was desired to use them to prepare counter-types of the prime prints while, on the contrary, on diazo compound sensitive products, they give perfect reproductions.

Such low density matrices for printing diazo compound sensitized lms would be useless for projection purposes.

As a practical indication, it is well known that when the gelatine side of a diapositive or transparency giving a good image on projection is .applied on very white paper, no detail can be described in the shadows; the image gives the impression of a much overexposed proof on bromide paper, while a matrix prepared according to the t conditions set forth in this specification would appear, when applied on white paper, as a bromide proof on paper properly exposed.

Of course, due to the large variety of the diazo compounds suitable for use, it would be impossible to determine in an absolute manner the proportions of diazo compound to be used, otherwise than by indicating that the salt amount should be such as to give an optical density superior to 1.6.

In practice, the method is to be checked as follows:

A sensitizing bath containing the4 diazo coinpound having been prepared, the operator will ascertain whether the concentration thereof is proper by dipping thereinto a small fragment of the pellicle tc be sensitized and by thoroughly developing the same without any previous exposure to the sun. Then he will measure the density thereof and correct the bath according to the result obtained.

The notion of density as applied to a coloured image may read somewhat ambiguous. It may be made more precise in the following manner.

` mitted is only oi. the incident light for those rays. v

The conclusions that are the object ot this speciilcation apply in the same conditions and by observing the same proportions to graphic papers which are based on the use of diazo derivatives and prepared especially in view o! reproducing not line engraving but process 1. In a method oi preparing diazo compound sensitized mms, comprising applying suiiicient diazo compound sensitized material to the nlm .to give a maximum optical density above 1.6, the steps of using as' matrices for printing the illms.

natural or toned silver salt prints or iilms developed with a gamma sufiiciently low in order that the darkest shadow be rendered on the diazo 4compound sensitized illm by a density lower than 3/4 of the maximum density which would be pro-y aooasia vided without any exposure to iight by said diano compound sensitized nlm.

2. In a method o! preparing cazo compound sensitized nlms, comprising applying suiiicient diazo derivatives to a regenerated cellulose nlm to give a. maximum steps of using as matrices for printing the films, natural or toned silver Asalt prints or nims developed with a gamma suiiicientlylow in order that the darkest shadow be rendered on the diazo compound sensitized nlm by a 'density lower than optical density above 1.6, the A 8/4 ot the maximum density which would be provided without any exposure to light by said diazo compound sensitized lm.

3. In a. method of preparing lmS sensitized with diazo compounds applied on a support o! "regenerated cellul the steps of using for printing, positive matrices oi silver salts; black or toned and developed with a gamma suii'iciently lowv in order that the darkest shadows bel rendered on the sensitive film with a density lower than 3/4 of the maximum density which would be provided without anyl exposure of the diazo compound sensitized film to light, the concentration of the nlm in diazo compound being fixed s0 that the gradation'oi the images obtained on the lm will be normal for the projection.

. PAUL VANET. 

